Active energy ray curable composition for coating optical disk and optical disk

ABSTRACT

The present invention relates to an active energy ray curable composition for coating optical disc, comprising a urethane (meth)acrylate compound having at least one amide group in the molecule, an ethylenically unsaturated compound other than the urethane (meth)acrylate compound and a photopolymerization initiator; and an optical disc having a cured coating layer obtained by curing the composition.

TECHNICAL FIELD

The present invention relates to an active energy ray curablecomposition for coating optical disc, and an optical disc, and moreparticularly, to an active energy ray curable composition capable offorming a transparent cured coating layer showing low volume shrinkagecoefficient in polymerization and having sufficient mechanical strength,and an optical disc having a cured coating layer particularlytransparent for blue light, obtained by curing the above-mentionedcurable composition.

BACKGROUND ART

Recently, there are used a lot of optical discs such as compact discs,once write type optical discs, magneto-optical discs and phase changetype optical discs as information recording media. These optical discsare generally produced by methods in which a thin metal film stackworking as a recording layer or light reflection layer is formed by asputtering method on a recording surface of a transparent resinsubstrate made of polycarbonate and the like on which fine patterns suchas pits and grooves have been formed, and for preventing deteriorationof these layers, a protective layer having a thickness of about 5 to 20μm is formed with a ultraviolet ray curable type resin.

On the other hand, recently, widely spreading as those having enhancedrecording capacity are, for example, DVD (digital video disc or digitalversatile disc) produced by bonding optical disc substrates having athickness of 0.6 mm, described in Japanese Patent Application Laid-Open(JP-A) No. 8-212597.

Further, JP-A No. 8-235638 suggests an optical disc as a high densityoptical disc having improved recording capacity than that of DVD andcapable of recording high quality video data and the like for a longperiod of time. This high density optical disc is an optical disc whichis obtained by forming a recording layer on a transparent or opaquesubstrate made of a plastic and the like then laminating an opticaltransmittance layer having a thickness of about 100 μm on the recordinglayer and to which recording light and/or reading light is directedthrough the optical transmittance layer. Regarding this high densityoptical disc, there is a suggestion, as described in JP-A No. 11-273147,of further increasing density by short wavelength recording utilizinglaser ray having a wavelength of, for example, 400 nm which is shorterthan that of red laser conventionally used for recording and/or readingof optical information media such as compact discs and DVD.

As methods of forming this optical transmittance layer, there are listed(1) a method in which a transparent film having a thickness of 100 μm ispasted on a recording layer using an adhesive, (2) a method in which anultraviolet ray curable resin placed on a recording layer is pushed tospread to obtain desired thickness with a flat transparent plate made ofglass and the like, and cured by irradiation with ultraviolet ray viathis plate, and the plate is released to give an optical transmittancelayer, (3) a method in which an ultraviolet ray curable resin is appliedon a recording layer by a spin coating method, then, irradiated withultraviolet ray to obtain an optical transmittance layer.

As the ultraviolet ray curable resin used for formation of such anoptical transmittance layer, there are listed, for example, compositionsdescribed in JP-A Nos. 3-131605 and 4-264167. There can also be usedultraviolet ray curable resins for transfer of optical disc stamper, forformation on a transparent substrate of tracking grooves described inJP-A Nos. 61-208646, 62-88156 and 5-59139.

However, when an optical transmittance layer of a high density typeoptical disc described above is formed using ultraviolet ray curableresins described in JP-A Nos. 3-131605, 4-264167, 61-208646 and62-88156, there is a practical problem that significant skew occurs onan optical disc since the ultraviolet ray curable resin has high volumeshrinkage coefficient. With respect to a composition described in JP-ANo. 5-59139, when a composition of ratio causing no skew is prepared,there occurs a problem that the resulting cured substance has poorhardness, leading to difficulty in making balance between hardness andskew. With a composition adopted in examples described in thispublication, significant skew occurs though hardness is high.

JP-A No. 54-127994 describes a coating composition containing a specificamide-modified urethane acrylate radiation-curable compound. However,this coating composition is used for formation of a protective coatingfilm of a vinyl cover, and is a composition used in the field utterlydifferent from a coating layer of an optical disc. Further, the objectof inclusion of a urethane acrylate in this coating composition is toimpart bending strength and tensile strength to a cured film, and basedon a viewpoint irrelevant to problems (e.g. volume shrinkage) specificto a coating layer of an optical disc as described above.

DISCLOSURE OF INVENTION

An object of the invention is to provide an active energy ray curablecomposition for coating optical disc, capable of forming a cured coatinglayer (protective layer) showing low volume shrinkage coefficient inpolymerization, having excellent transparency, and having excellenthardness, ability to protect a recording layer and mechanicalproperties, and an optical disc having a cured coating layer obtained bycuring this composition.

The present invention relates to an active energy ray curablecomposition for coating optical disc, comprising aurethane(meth)acrylate compound (A) having at least one amide group inthe molecule, an ethylenically unsaturated compound (B) other than theurethane(meth)acrylate compound (A) and a photopolymerization initiator(C); and an optical disc having a cured coating layer obtained by curingthe composition.

Further, the present invention relates to an optical disc comprising asubstrate carrying thereon a recording layer and a cured coating layerlaminated in this order in which the cured coating layer acts as anincident side surface for recording light and/or reading light, whereinthe cured coating layer is a layer obtained by curing a curablecomposition having a volume shrinkage coefficient of 7.5% or less,having a pencil hardness of 2B or more, and having a beam transmittancein the wavelength range from 380 to 800 nm of 75% or more.

BEST MODES FOR CARRYING OUT THE INVENTION

The active energy ray curable composition of the present invention willbe illustrated.

The active energy ray curable composition of the present invention canform a transparent cured coating layer for optical disc, having lowvolume shrinkage coefficient and having mechanical strength.

The urethane(meth)acrylate compound (A) having at least one amide groupin the molecule used in the composition of the present invention is acomponent imparting a low shrinkage property to the composition anddurabilities such as hardness and impact resistance to the resultingcured coating layer (protective layer). In the present invention,(meth)acrylate is a generic name for acrylate and methacrylate.

The urethane(meth)acrylate compound (A) is not particularly restricted,and in the case of formation of a cured coating layer having a thicknessof about 100 μm, for example, urethane(meth)acrylates obtained byreacting the following components (a1) to (a4) are suitable:

-   -   (a1) Amide-containing compounds having at least one amide group        and at least two hydroxy groups in the molecule,    -   (a2) Poly-hydric alcohol compounds other than the        above-mentioned component (a1),    -   (a3) Diisocyanate compounds,    -   (a4) Hydroxy group-containing (meth)acrylates.

The amide-containing compound (a1) having at least one amide group andat least two hydroxy groups in the molecule is a component having anaction of improving mechanical strength (toughness) while maintainingthe low shrinkage property of the cured coating layer. As this component(a1), there are listed, for example, reaction products of cyclichydroxycarboxylates with ammonia or amine compounds containing oneprimary or secondary amino nitrogen.

Specific examples of the cyclic hydroxycarboxylates includeγ-butyrolactone, δ-valerolactone and ε-caprolactone. These can be usedsingly or in combination of two or more. Of them, γ-butyrolactone andδ-valerolactone are particularly preferable.

Specific examples of the amine compounds containing one primary orsecondary amino nitrogen include ethanolamine, diethanolamine,N-methylethanolamine, N-ethyl-ethanolamine, N-phenylethanolamine,2-amino-1-butanol, 2-amino-2-ethyl-1,3-propanediol, 6-amino-1-hexanol,1,4-diaminobutane, 1,2-diaminocyclohexane and 1,10-diaminodecane. Thesecan be used singly or in combination of two or more. Of them,ethanolamine, diethanolamine and N-methylethanolamine are particularlypreferable from the standpoint of cost.

The reaction of a cyclic hydroxycarboxylate with ammonia or compoundcontaining one primary or secondary amino nitrogen is conducted, forexample, by mixing them in equimolar amounts and heating them at about100° C. for 6 to 24 hours.

As the particularly preferable component (a1),N-methyl-N-(2-hydroxyethyl)-3-hydroxypropylamide and the like arelisted.

The component (a2) is a poly-hydric alcohol compounds excluding thecomponents (a1) described in detail above, and has an action to improvethe flexibility and elongation of a cured substance of aurethane(meth)acrylate compound (A).

As the component (a2), for example, commercially available variouspoly-hydric alcohol compounds can be used. Specific examples thereofinclude polyether diols such as polyethylene glycol, polypropyleneglycol, polybutylene glycol and 1-methylbutylene glycol; poly-hydricalcohols such as neopentyl glycol, ethylene glycol, diethylene glycol,propylene glycol, 1,6-hexanediol, 1,4-butanediol, 1,9-nonanediol,1,10-decanediol, 3-methylpentanediol, 2,4-diethylpentanediol,tricyclodecanedimethanol, 1,4-cyclohexanedimethanol,1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, cyclohexanediol,hydrogenated bisphenol A and bisphenol; polyether-modified diolsobtained by adding alkylene oxides such as ethylene oxide, propyleneoxide and butylenes oxide to the above-mentioned poly-hydric alcohols;polyester diols such as diol compounds obtained by reaction of theabove-mentioned poly-hydric alcohols with poly-basic acids such assuccinic acid, phthalic acid, hexahydrophthalic acid, terephthalic acid,adipic acid, azelaic acid and tetrahydrophthalic acid or acid anhydridesof these poly-basic acids, polycaprolactonediol compounds obtained byreaction of the above-mentioned poly-hydric alcohols with lactones suchas ε-caprolactone, γ-butyrolactone, γ-valerolactone and δ-valerolactone,further, caprolactone-modified polyester diol compounds obtained byreaction of the above-mentioned poly-hydric alcohols and poly-basicacids with lactones such as ε-caprolactone, γ-butyrolactone,γ-valerolactone and δ-valerolactone; polycarbonate diols such asaromatic polycarbonate diol and aliphatic polycarbonate diol;polybutadienediols; and other compounds. These can be used singly or incombination of two or more.

In view of the low shrinkage property of the resulting cured substance,the weigh-average molecular weight of the component (a2) is preferably300 or more. From the standpoint of decreasing in the viscosity of thecomposition, the weigh-average molecular weight is preferably 2000 orless. Further, it is particularly preferable to use at least one diolcompound selected from the group consisting of polyether diols,polyester diols and polycarbonate diols, among the above-mentionedspecific examples, from the standpoint of excellent strength elongationbalance. Particularly preferable are polybutylene glycol,polycaprolactone diol and aliphatic polycarbonate diols.

The component (a3) is a diisocyanate compound. This component (a3) is acomponent not only introducing a urethane bond into the above-mentionedtwo alcohol components [components (a1) and (a2)] to increase toughnessbut also manifesting a urethane(meth)acrylate synthesis reaction foradding a hydroxy group-containing (meth)acrylate [component (a4)].

Specific examples of the component (a3) include isophorone diisocyanate,bis(4-isocyanatocyclohexyl)methane, bis(4-isocyanatophenyl)methane,bis(3-chloro-4-isocyanatophenyl)methane, 2,4-tolylene diisocyanate,2,6-tolylene diisocyanate, 1,2-xylylene diisocyanate, 1,4-xylylenediisocyanate, 1,2-hydrogenated xylylene diisocyanate, 1,4-hydrogenatedxylylene diisocyanate, tetramethylxylylene diisocyanate, hydrogenatedtetramethylxylylene diisocyanate, naphthalene diisocyanate,hexamethylene diisocyanate and norbornane diisocyanate. These can beused singly or in combination of two or more.

Of them, preferable are isophorone diisocyanate,bis(4-isocyanatocyclohexyl)methane, 2,4-tolylene diisocyanate,2,6-tolylene diisocyanate, 1,2-xylylene diisocyanate, 1,4-xylylenediisocyanate, 1,2-hydrogenated xylylene diisocyanate, 1,4-hydrogenatedxylylene diisocyanate, hydrogenated tetramethylxylylene diisocyanate andnorbornane diisocyanate.

Further, diisocyanate compounds having an alicyclic skeleton areparticularly preferable such as isophorone diisocyanate,bis(4-isocyanatocyclohexyl)methane, 1,2-hydrogenated xylylenediisocyanate, 1,4-hydrogenated xylylene diisocyanate, hydrogenatedtetramethylxylylene diisocyanate and norbornane diisocyanate, since theycan impart excellent toughness and non yellowing property to a curedcoating layer. It is preferable to use a diisocyanate compound having ahydrolysable chlorine amount of 100 ppm or less from the standpoint ofimprovement in an ability of protecting a recording layer of an opticaldisc.

The component (a4) is a hydroxy group-containing (meth)acrylate, and isa component imparting radical reactivity by addition thereof to the endof a polyurethane precursor. Specific examples thereof include2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate,4-hydroxybutyl(meth)acrylate, 6-hydroxyhexyl(meth)acrylate, cyclohexanedimethanol mono(meth)acrylate, adduct of 2-hydroxyethyl(meth)acrylateand caprolactone, trimethylolpropane diacrylate, pentaerythritoltriacrylate and dipentaerythritol pentaacrylate. These can be usedsingly or in combination of two or more. Of them, particularlypreferable are 2-hydroxyethyl(meth)acrylate,2-hydroxypropyl(meth)acrylate and 4-hydroxybutyl(meth)acrylate from thestandpoint of decreasing in the viscosity of a composition.

The specific method of synthesizing a urethane(meth)acrylate compound(A) is not particularly restricted and various synthesis methodsconventionally known can be used. For example, 0.8 to 1.2 mol equivalentof a mixture of a component (a1) and a component (a2), and di-n-butyltindilaurate acting as a synthesis catalyst in an amount of 50 to 300 ppmbased on the final total amount, are charged in a synthesis vessel,these are heated at 40 to 80° C., and 2 mol equivalent of diisocyanate,component (a3) is added while stirring, to obtain an isocyanate-endedpolyurethane as a precursor. To this, 0.8 to 1.2 mol equivalent of acomponent (a4) is further dropped, and kept at 60 to 80° C. for 4 to 8hours, to obtain a urethane(meth)acrylate compound (A).

The molar equivalent referred to here is a number obtained bymultiplying the molar number of a compound used by the number offunctional groups relating to the above-mentioned synthesis reaction.

In the composition of the present invention, the use proportion of acomponent (A) is not particularly restricted, and preferably from 20 to80 parts by weight, more preferably from 25 to 75 parts by weight andparticularly preferably from 30 to 70 parts by weight based on 100 partsby weight of the total amount of components (A) and (B). Particularly,the use proportion of a component (A) is preferably 15 parts by weightor more from the standpoint of the low shrinkage property of acomposition, and preferably 75 parts by weight or less for decreasingthe viscosity of a composition to obtain excellent workability ofpainting on an optical disc.

The component (B) used in the composition of the present invention is anethylenically unsaturated compound other than the component (A), and isa component controlling the composition to have viscosity suitable forpainting, further, improving a curing property and the durability of acured coating layer.

This component (B) is not particularly restricted, and conventionallyknown various ethylenically unsaturated compounds can be used singly orin combination of two or more. Of them, bisphenol typeepoxy(meth)acrylate compounds (b1) and/or compounds (b2) of thefollowing generation formula (I) are preferably used.

wherein, X₁ and X₂ represent an acryloyloxy group or methacryloyloxygroup, X₃ represents a hydroxy group, acryloyloxy group ormethacryloyloxy group, and R₁, R₂ and R₃ represent an alkyl group having1 to 4 carbon atoms.

As the specific examples of the bisphenol type epoxy(meth)acrylatecompound (b1), listed are bisphenol type epoxy(meth)acrylates obtainedby reacting unsaturated mono-basic acids such as (meth)acrylic acid,(meth)acrylic acid dimmer and caprolactone-modified (meth)acrylic acidwith a bisphenol type epoxy resin obtained by a condensation reaction ofbisphenols such as bisphenol A, bisphenol F, bisphenol S andtetrabromobisphenol A with epichlorohydrin. Of them, preferable arebisphenol A type epoxy(meth)acrylate and bisphenol F typeepoxy(meth)acrylate because of excellent balance of viscosity and heatresistance.

Since the resulting composition has low viscosity and shows low volumeshrinkage coefficient in polymerization, bisphenol type epoxy(meth)acrylates having a molecular weight in the range from 800 to 5000are more preferable. When the molecular weight is 800 or more, volumeshrinkage coefficient in polymerization can be lowered to prevent skewof an optical disc. When 5000 or less, the viscosity of a compositioncan be lowered to improved painting workability.

For suppressing corrosion of a recording layer of an optical disc, it ispreferable that an epoxy resin used as a raw material of anepoxy(meth)acrylate contains no chlorine. When chlorine is contained,the total chlorine content of an epoxy resin is preferably 2000 ppm orless, more preferably 1500 ppm or less.

Specific examples of the compound (b2) of the general formula (I)include bis(2-acryloyloxyethyl)hydroxyethyl isocyanurate,bis(2-acryloyloxypropyl)hydroxypropyl isocyanurate,bis(2-acryloyloxybutyl)hydroxybutyl isocyanurate,bis(2-methacryloyloxyethyl)hydroxyethyl isocyanurate,bis(2-methacryloyloxypropyl)hydroxypropyl isocyanurate,bis(2-methacryloyloxybutyl)hydroxybutyl isocyanurate,tris(2-acryloyloxyethyl)isocyanurate,tris(2-acryloyloxypropyl)isocyanurate,tris(2-acryloyloxybutyl)isocyanurate,tris(2-methacryloyloxyethyl)isocyanurate,tris(2-methacryloyloxypropyl)isocyanurate andtris(2-methacryloyloxybutyl)isocyanurate. These can be used singly or incombination of two or more. Of them,tris(2-acryloyloxyethyl)isocyanurate showing an excellent curingproperty is preferably used, and it is more referable to use a mixtureobtained by mixing bis(2-acryloyloxyethyl)hydroxyethyl isocyanurate inan amount of 0.01 to 40% by weight withtris(2-acryloyloxyethyl)isocyanurate, from the standpoint lowtemperature storage stability.

Specific examples of the ethylenically unsaturated compound (B) otherthan the above-mentioned components (b1) and (b2) includepoly-functional (meth)acrylates such as trimethylolpropanetri(meth)acrylate, trisethoxylated trimethylolpropane tri(meth)acrylate,ditrimethylolpropane tetra(meth)acrylate, pentaerythritoltri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ethoxylatedpentaerythritol tri(meth)acrylate, ethoxylated pentaerythritoltetra(meth)acrylate, dipentaerythritol penta(meth)acrylate,dipentaerythritol penta(meth)acrylate, dipentaerythritolhexa(meth)acrylate, caprolactone-modified dipentaerythritolpenta(meth)acrylate, caprolactone-modified dipentaerythritolhexa(meth)acrylate, C₂₋₅ aliphatic hydrocarbon-modifiedtrimethylolpropane triacrylate, C₂₋₅ aliphatic hydrocarbon-modifieddipentaerythritol penta(meth)acrylate and C₂₋₅ aliphatichydrocarbon-modified dipentaerythritol tetra(meth)acrylate;

di(meth)acrylates such as ethylene glycol di(meth)acrylate, 1,3-butyleneglycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, nonanediol di(meth)acrylate, neopentyl glycoldi(meth)acrylate, methylpentanediol di(meth)acrylate, diethylpentanedioldi(meth)acrylate, neopentyl glycol hydroxypivalate di(meth)acrylate,tetraethylene glycol di(meth)acrylate, tripropylene glycoldi(meth)acrylate, polybutylene glycol di(meth)acrylate,tricyclodecanedimethanol di(meth)acrylate, cyclohexanedimethanoldi(meth)acrylate, polyethoxylated cyclohexanedimethanoldi(meth)acrylate, polypropoxylated cyclohexanedimethanoldi(meth)acrylate, polyethoxylated bisphenol A di(meth)acrylate,polypropoxylated bisphenol A di(meth)acrylate, hydrogenated bisphenol Adi(meth)acrylate, polyethoxylated hydrogenated bisphenol Adi(meth)acrylate, polypropoxylated hydrogenated bisphenol Adi(meth)acrylate, bisphenoxyfluorene ethanol di(meth)acrylate, neopentylglycol-modified trimethylolpropane di(meth)acrylate, di(meth)acrylate ofε-caprolactone adduct (n+m=2 to 5) of neopentyl glycol hydroxypivalate,di(meth)acrylate of γ-butyrolactone adduct (n+m=2 to 5) of neopentylglycol hydroxypivalate, di(meth)acrylate of caprolactone adduct (n+m=2to 5) of neopentyl glycol, di(meth)acrylate of caprolactone adduct(n+m=2 to 5) of butylene glycol, di(meth)acrylate of caprolactone adduct(n+m=2 to 5) of cyclohexanedimethanol, di(meth)acrylate of caprolactoneadduct (n+m=2 to 5) of dicyclopentanediol, di(meth)acrylate ofcaprolactone adduct (n+m=2 to 5) of bisphenol A, di(meth)acrylate ofcaprolactone adduct (n+m=2 to 5) of hydrogenated bisphenol A anddi(meth)acrylate of caprolactone adduct (n+m=2 to 5) of bisphenol F;

(meth)acrylates such as 2-hydroxyethyl(meth)acrylate,2-hydroxypropyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate,tetrahydrofurfuryl(meth)acrylate, phenoxyethyl(meth)acrylate,cyclohexyl(meth)acrylate, isobonyl(meth)acrylate,norbornyl(meth)acrylate, 2-methyl-2-norbornylmethyl(meth)acrylate,trimethylolpropaneformal(meth)acrylate,2-methyl-2-ethyl-1,3-dioxolanyl(meth)acrylate, adamantyl(meth)acrylate,benzyl(meth)acrylate, phenyl(meth)acrylate,dicyclopentenyl(meth)acrylate, dicyclopentenyl(meth)acrylate,tetracyclododecanyl(meth)acrylate, cyclohexanedimethanolmono(meth)acrylate, 2-methoxyethyl(meth)acrylate,3-methoxybutyl(meth)acrylate, methoxytriethylene glycol(meth)acrylate,butoxyethyl(meth)acrylate and methoxydipropylene glycol(meth)acrylate;

vinyl ester monomers such as vinyl acetate, vinyl butyrate,N-vinylformamide, N-vinylacetamide, N-vinyl-2-pyrrolidone,N-vinylcaprolactam and divinyl adipate;

vinyl ethers such as ethyl vinyl ether and phenyl vinyl ether;

acrylamides such as acrylamide, N,N-dimethylacrylamide,N,N-dimethylmethacrylamide, N-methylolacrylamide,N-methoxymethylacrylamide, N-butoxymethylacrylamide,N-t-butylacrylamide, acryloylmorpholine, hydroxyethylacrylamide andmethylenebisacrylamide;

polyester poly(meth)acrylates obtained by reaction of a poly-basic acidsuch as phthalic acid, succinic acid, hexahydrophthalic acid,tetrahydrophthalic acid, terephthalic acid, azelaic acid and adipic acidwith a poly-hydric alcohol such as ethylene glycol, hexanediol,polyethylene glycol and polytetramethylene glycol, and (meth)acrylicacid or its derivative;

urethane poly(meth)acrylates other than the components (A), obtained byreacting a single body or a mixture of two or more of organicdiisocyanate compounds with a single-body or a mixture of two or more ofhydroxyl group-containing (meth)acrylates having one or more(meth)acryloyloxy groups and one hydroxyl group in the molecule;

urethane poly(meth)acrylates other than the components (A), obtained byadding an organic diisocyanate compound to a hydroxyl group of one ofalkane diols, polyether diols, polybutadiene diol, polyester diols,polycarbonate diols and spiroglycol compounds or of alcohols composed ofa mixture of two or more of them, and reacting a hydroxylgroup-containing (meth)acrylate containing one or more (meth)acryloyloxygroups and one hydroxyl group in the molecule with the remainingisocyanate groups.

These can be used singly or in combination of two or more. Of them,compounds having a cyclic structure in the molecule are preferablebecause of excellent water resistance. Specific examples of thesepreferable compounds include compounds such as tricyclodecanedimethanoldi(meth)acrylate, polyethoxylated bisphenol A di(meth)acrylate,polypropoxylated bisphenol A di(meth)acrylate, polyethoxylatedhydrogenated bisphenol A di(meth)acrylate, polypropoxylated hydrogenatedbisphenol A di(meth)acrylate, polyethoxylated cyclohexanedimethanoldi(meth)acrylate, polypropoxylated cyclohexanedimethanoldi(meth)acrylate, tetrahydrofurfuryl(meth)acrylate,phenoxyethyl(meth)acrylate, cyclohexyl(meth)acrylate,isobonyl(meth)acrylate, norbornyl(meth)acrylate,2-methyl-2-norbornylmethyl(meth)acrylate,trimethylolpropaneformal(meth)acrylate,2-methyl-2-ethyl-1,3-dioxolanylmethyl(meth)acrylate,adamantyl(meth)acrylate, benzyl(meth)acrylate, phenyl(meth)acrylate,dicyclopentenyl(meth)acrylate, dicyclopentenyl(meth)acrylate andtetracyclododecanyl(meth)acrylate.

In the composition of the present invention, the use ratio of thecomponent (B) is not particularly restricted, and preferably from 20 to80 parts by weight, more preferably from 25 to 75 parts by weight basedon 100 parts by weight of the total amount of the components (A) and(B). Particularly, the use ratio of the component (B) is preferably 20parts by weight or more for decreasing the viscosity of a compositionand for enhancing painting workability on an optical disc, andpreferably 80 parts by weight or less from the standpoint of the lowshrinkage property of a composition.

When the component (B) contains the above-mentioned component (b1)and/or the component (b2), the total use ratio of the components (b1)and (b2) is preferably from 5 to 40 parts by weight, more preferablyfrom 5 to 30 parts by weight based on 100 parts by weight of the totalamount of the components (A) and (B). When this use ratio is 5 parts byweight or more, the mechanical strength of a cured coating layer tendsto become excellent, and when 40 parts by weight or less, there is atendency that the liquid viscosity of a composition decreases andpainting workability on an optical disc is improved.

The component (C) used in the composition of the present invention is aphotopolymerization initiator, and by inclusion of this, a curedsubstance can be efficiently obtained by a ultraviolet ray curingmethod.

Specific examples of the component (C) include benzophenone,4,4-bis(diethylamino)benzophenone, 2,4,6-trimethylbenzophenone,methyl-o-benzoyl benzoate, 4-phenylbenzophenone, t-butylanthraquinone,2-ethylanthraquinone, diethoxyacetophenone,2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethylketanol,1-hydroxycyclohexyl-phenylketone, benzoin methyl ether, benzoin ethylether, benzoin isopropyl ether, benzoin isobutyl ether,2-methyl-[4-(methylthio)phenyl]-2-morpholino-1-propanone,2-benzyl-2-dimethylamino-1-(4-morpholino-phenyl)-butanone-1,diethylthioxanetone, isopropylthioxanetone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide,bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide,bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide and methylbenzoylformate.

For example, when the wavelength of laser used for reading of an opticaldisc is in the range from 380 to 800 nm, it is preferable toappropriately select the kind and use amount of a photopolymerizationinitiator so that laser ray necessary for reading can pass a curedcoating layer sufficiently. In this case, it is particularly preferableto use a short wavelength-photosensitive type photopolymerizationinitiator so that a cured coating layer does not absorb blue laser ray.

Specific examples of this short wavelength-photosensitive typephotopolymerization initiator include benzophenone,2,4,6-trimethylbenzophenone, methyl-o-benzoyl benzoate,4-phenylbenzophenone, diethoxyacetophenone,2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal,1-hydroxycyclohexyl-phenylketone, benzoin methyl ether, benzoin ethylether, benzoin isopropyl ether, benzoin isobutyl ether and, methylbenzoyl formate. These can be used singly or in combination of two ormore.

In the composition of the present invention, the use ratio of thecomponent (C) is not particularly restricted, and preferably from 0.001to 10 parts by weight, more preferably from 0.01 to 5 parts by weightbased on 100 parts by weight of the total amount of the components (A)and (B). Particularly, the use ratio of the component (C) is preferably0.001 part by weight or more from the standpoint of the curing propertyof a coated film, and preferably 10 parts by weight or less from thestandpoints of the deep part curing property of a coated film,prevention of coloration of a cured substance, and reading ofinformation of a recording layer by blue laser.

Further, in the composition of the present invention, conventionallyknown various photo-sensitizers can also be added, if necessary, such asmethyl 4-dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, amyl4-dimethylaminobenzoate and 4-dimethylaminoacetophenone. Further, ifnecessary, conventionally known various additives may also becompounded, such as thermoplastic polymers, slipping agents, levelingagents, antioxidants, photo-stabilizers, ultraviolet absorbers,polymerization inhibitors, silane coupling agents, inorganic fillers,organic fillers and inorganic fillers having an organic-treated surface,in an amount not deteriorating its abilities.

Particularly, it is preferable to use an antioxidant orphoto-stabilizer, to prevent yellowing of a cured film in use for a longperiod of time and to avoid disturbance in reading or writing of anoptical disc.

As the antioxidant or photo-stabilizer, those commercially available canbe used. Specific examples of the commercially available productsinclude products of Sumitomo Chemical Co., Ltd., Sumilizer BHT,Sumilizer S, Sumilizer BP-76, Sumilizer MDP-S, Sumilizer GM, SumilizerBBM-S, Sumilizer WX-R, Sumilizer NW, Sumilizer BP-179, Sumilizer BP-101,Sumilizer GA-80, Sumilizer TNP, Sumilizer TPP-R, Sumilizer P-16;products of Asahi Denka Kogyo K.K., Adekastab AO-20, Adekastab AO-30,Adekastab AO-40, Adekastab AO-50, Adekastab AO-60AO-70, Adekastab AO-80,Adekastab AO-330, Adekastab PEP-4C, Adekastab PEP-8, Adekastab PEP-24G,Adekastab PEP-36, Adekastab HP-10, Adekastab 2112, Adekastab 260,Adekastab 522A, Adekastab 329K, Adekastab 1500, Adekastab C, Adekastab135A, Adekastab 3010; products of Chiba Specialty Chemicals K.K.,Tinubin 770, Tinubin 765, Tinubin 144, Tinubin 622, Tinubin 111, Tinubin123, Tibubin 292; products by Hitachi Chemical Co., Ltd., FancrylFA-711M, FA-712 HM and the like (these are all trade names).

The addition amount these antioxidants and photo-stabilizers is notparticularly restricted, and preferably from 0.001 to 2 parts by weight,more preferably from 0.01 to 1 part by weight based on 100 parts byweight of the total amount of the components (A) and (B).

The viscosity of the composition of the present invention is preferablyfrom 1000 to 10000 mPa·s at 25° C., and more preferably from 2000 to8000 mPa·s. When this viscosity is 1000 mPa·s or more, paintingworkability is excellent, and when 10000 mPa·s or less, handing of acomposition is excellent. When in the range from 2000 to 8000 mPa·s, acoated layer having a thickness of 100 μm can be obtained byspin-coating in a short period of time.

The painting method of the composition of the present invention is notparticularly restricted, and may advantageously be conducted by knownmethods, and preferable is a spin coater method from the standpoint ofthe productivity of an optical disc.

For curing a coated film of the composition of the present invention,the membrane may be advantageously irradiated with active energy rayssuch as, for example, α, β and γ rays by a known method. Particularly,ultraviolet ray is preferably used. The ultraviolet ray generationsource may be a ultraviolet ray lamp generally used from the standpointsof practicability and economy. Specific examples of the ultraviolet lampinclude a low pressure mercury lamp, high pressure mercury lamp, superhigh pressure mercury lamp, xenon lamp and metal halide lamp.Irradiation with light energy may be conducted in air or in an inert gassuch as nitrogen and argon.

Next, the optical disc of the present invention will be illustrated indetail.

The optical disc of the invention relates to an optical disc having acured coating layer obtained by curing the active energy ray curablecomposition of the present invention described above; or an optical disccomprising a substrate carrying thereon a recording layer and a curedcoating layer laminated in this order in which the cured coating layeracts as an incident side surface for recording light and/or readinglight, wherein the cured coating layer is a layer obtained by curing acurable composition having a volume shrinkage coefficient of 7.5% orless, having a pencil hardness of 2B or more, and having a beamtransmittance in the wavelength range from 380 to 800 nm of 75% or more.

The cured coating layer herein referred indicates all cured coatinglayers constituting optical discs, such as an optical transmittancelayer of an optical disc, an adhesive and optical transmittance layer ofmulti-layer recording type discs such as DVD. This cured coating layeris preferably apparently transparent so that reading disturbance doesnot occur when reading and writing of data of a recording layer areconducted.

The active energy ray curable composition having a volume shrinkagecoefficient of 7.5% or less forming this cured coating layer is notparticularly restricted and listed are, for example, compositions of thepresent invention as described in detail above.

In the present invention, liquid specific gravity (d1) before curing at20° C. and specific gravity (d2) at 20° C. of a cured coating layerobtained by curing are measured, and a value calculated according to thefollowing numerical formula is volume shrinkage coefficient (%).Volume shrinkage coefficient (%)=[(d2−d1)/d2]×100  (1)

When the volume shrinkage coefficient is over 7.5%, disadvantages easilyoccur such as poor close adhesiveness with a recording layer andsignificant skew of an optical disc by shrinkage in curing, causing atendency of difficulty in recording and reading.

The surface hardness of a cured coating layer of an optical disc of thepresent invention is preferably 2B or more in terms of pencil hardness.Particularly, when a hard coat layer is not formed on a cured coatinglayer, the hardness is more preferably B or more. The pencil hardnessherein referred to is a value obtained by a method according to JISK-5400. When this pencil hardness is softer than 2B, the surface of acured coating layer is easily scratched, leading to a tendency to causewriting or reading error of an optical disc.

The beam transmittance of a cured coating layer of the optical disc ofthe present invention in the wavelength range of 380 to 800 nm ispreferably 75% or more, more preferably 80% or more, for preventingreading or writing error. The wavelength of laser ray used for readingor writing of the optical disc of the present invention is notparticularly restricted, and in general, it is used for reading orwriting of an optical disc. Laser ray within the wavelength range from380 to 800 nm is preferable, and violet laser ray having a wavelengtharound 400 nm is preferable particularly since the recording capacity ofan optical disc can be increased.

The thickness of a cured coating layer is not particularly restrictedproviding desired properties are obtained, and preferably from 20 to 200μm, more preferably from 50 to 150 μm. When this thickness is 20 μm ormore, oxidation deterioration or deterioration by water of a recordinglayer can be suppressed. When 200 μm or less, skew of an optical disccan be suppressed.

For forming a cured coating layer, it may be recommendable that, forexample, a uniform painted membrane of an active energy ray curablecomposition is formed on the recording layer side of a supportingsubstrate having a recording layer, and the membrane is irradiated withactive energy ray for curing.

The glass transition temperature of a cured coating layer is notparticularly restricted, and preferably 50° C. or more, more preferably60° C. or more, in view of use in environments requiring heat resistancesuch as automobile application.

On the optical disc of the present invention, a hard coat layer and thelike may be appropriately laminated on a cured coating layer, for thepurpose of further improving weather resistance and surface hardness.

The composition for forming a hard coat layer is not particularlyrestricted, and conventionally known various hard coat compositions canbe used such as, for example, acrylic hard coat materials and silicafine particle-containing hard coat materials. It is preferable that thiscomposition is painted and cured to form a hard coat layer having athickness of 0.1 to 7 μm, preferably 0.3 to 5 μm. In this case, the beamtransmittance in the wavelength range from 380 to 800 nm through twolayers of a cured coating layer and a hard coat layer is preferably 70%or more, more-preferably 75% or more.

As the specific examples of the acrylic hard coat material, mentionedare hard coat compositions composed of 20 to 60% by weight of a compoundhaving three or more (meth)acryloyl groups in the molecule and 40 to 80%by weight of other ethylenically unsaturated compounds.

Particularly, when a high density optical disc which shows increase inreading error only in the presence of slight scratch is produced, it ispreferable to use silica fine particle-containing hard coat materials.Namely, it is preferable that, on a cured coating layer of an opticaldisc, colloidal silica fine particles (d1) and a hydrolysis product ofan organic silane compound (d2) are condensed to obtain a curablecomposition containing organic-coated silica (D) which is cured to forma hard coat layer. It is more preferable that a curable compositioncontaining this organic-coated silica (D) and ethylenically unsaturatedcompound (E) is cured, to form a hard coat layer. The organic-coatedsilica (D) is a component imparting abrasion resistance and durabilityto a hard coat layer.

The colloidal silica fine particle (d1) is not particularly restricted,and for example, there can be used those prepared by dispersing ultrafine particles of inorganic silic acid having primary particle size of 1to 200 nm, preferably 5 to 80 nm in water or an organic solvent. Whenthe primary particle size is 1 nm or more, there is a tendency thatgelling is not cause in reacting with the component (d2), and when 200nm or less, there is a tendency that the transparency of a hard coatlayer becomes excellent.

The organic silane compound used in the hydrolysis product (d2) of anorganic silane compound is not particularly restricted, andconventionally known various organic silane compounds can be used.Specific examples thereof include methyltrimethoxysilane,dimethyldimethoxysilane, phenyltrimethoxysilane,diphenyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane,phenyltriehtoxysilane, diphenyldiethoxysilane, styryltrimethoxysilane,styryltriethoxysilane, hexyltrimethoxysilane, decyltrimethoxysilane,vinyltris(3-methoxyethoxy)silane, vinyltriethoxysilane,vinyltrimethoxysilane, 3-methacryloyloxypropyltrimethoxysilane,3-acryloyloxypropyltrimethoxysilane,3-methacryloyloxypropyltriethoxysilane,β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,3-glycidoxypropyltrimethoxysilane,3-glycidoxypropylmethyldiethoxysilane,3-methacryloyloxypropylmethyldiethoxysilane,N-β(aminoethyl)γ-aminopropyltrimethoxysilane,N-β(aminoethyl)γ-aminopropylmethyldimethoxysilane,3-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane,3-mercaptopropyltrimethoxysilane, 3-chloropropyltrimethoxysilane and3-isocyanatopropyltriethoxysilane. These can be used singly or incombination of two or more.

Further, silane compounds obtained by adding (meth)acrylic acid to anepoxy group or glycidyl group of these compounds, silane compoundsobtained by Michael—adding a compound having two (meth)acryloyloxygroups to an amino group of these compounds, silane compounds obtainedby adding a compound having a (meth)acryloyloxy group and an isocyanategroup to an amino group or mercapto group of these compounds, silanecompounds obtained by adding a compound having a (meth)acryloyloxy groupand a hydroxyl group to an isocyanate group of these compounds can alsobe used.

As the organic silane compound used in this hydrolysis product (d2),most preferable are monomers (organic silane compounds) of the followinggeneral formula (II):

wherein, X represents a methacryloyloxy group, acryloyloxy group, styrylgroup or vinyl group, R₄ represents a direct bond or a linear orbranched alkyl group having 1 to 8 carbon atoms, R₅ and R₆ represent alinear or branched alkyl group having 1 to 8 carbon atoms, a representsan integer of 1 to 3, b represents an integer of 0 to 2, and a+brepresents an integer of 1 to 3.

When a monomer of the general formula (II) is hydrolyzed to give asilanol compound, and the silanol compound is condensed with colloidalsilica fine particles (d1), organic-coated silica (D) is obtained. Theorganic-coated silica (D) obtained by using a monomer of the generalformula (II) shows a photo-curing property enabling formation of achemical bond with an ethylenically unsaturated compound (E). Namely, byuse of a monomer of the general formula (II), compatibility of thecomponent (D) and the component (E) is improved, and toughness can beimparted to the resulting cured coating layer.

Specific examples of the monomer of the general formula (II) include3-methacryloyloxypropyltrimethoxysilane,3-acryloyloxypropyltrimethoxysilane,2-methacryloyloxyethyltrimethoxysilane,2-acryloyloxyethyltrimethoxysilane,3-methacryloyloxypropyltriethoxysilane,3-acryloyloxypropyltriethoxysilane,2-methacryloyloxyethyltriethoxysilane,2-acryloyloxyethyltriethoxysilane,3-methacryloyloxypropylmethyldimethoxysilane,3-acryloyloxypropylmethyldimethoxysilane, styryltrimethoxysilane,styryltriethoxysilane and vinyltrimethoxysilane, vinyltriethoxysilane.These can be used singly or in combination of two or more. Of them,3-methacryloyloxypropylriethoxyilane,3-acryloyloxypropyltrimethoxysilane,3-methacryloyloxypropyltriethoxysilane,3-acryloyloxypropylrithoxysilane, vinyltrimethoxysilane andvinyltriethoxysilane are particularly preferable in excellent reactivitywith the component (E).

The organic-coated silica (D) can be produced by, for example, in thepresence of colloidal silica fine particles (d1) and a hydrolysisproduct (d2) of an organic silane compound, azeotropically distilling adispersion medium of the colloidal silica fine particles (d1) togetherwith a non-polar solvent such as toluene under normal pressure orreduced pressure to substitute the dispersion medium by a non-polarsolvent, then, heating them to cause reaction. The term “in the presenceof colloidal silica fine particles (d1) and a hydrolysis product (d2) ofan organic silane compound” herein referred to means a conditionobtained by the following two methods (1) and (2) when the hydrolysisproduct (d2) of an organic silane compound is a silanol compoundobtained by hydrolysis of a monomer of the general formula (II).

(1) A method in which the component (d1) and a monomer of the generalformula (II) are mixed, and a hydrolysis catalyst is added to this, andhydrolysis is caused by normal methods such as stirring under normaltemperature or heating, and the like, to provide coexistence of thecomponent (d1) and the component (d2).

(2) A method in which the component (d2) previously obtained byhydrolysis of a monomer of the general formula (II), and the component(d1) are mixed, to cause coexistence.

Further, to the product obtained by the above-mentioned methods (1) and(2), 0.5 to 6 mol of water of 0.001 to 0.1 N hydrochloric acid or ahydrolysis catalyst such as an acetic acid aqueous solution is added,per mol of a monomer of the general formula (I), in the presence orabsence of an organic solvent such as an alcohol solvent (in the case ofthe above-mentioned method (1), the component (d1) is also present), andthe mixture is stirred under heat while removing an alcohol generated byhydrolysis out of the system. Thus, a hydrolysis product (d2) can beproduced.

Next, a condensation reaction of the component (d1) and the component(d2) is conducted, to obtained organic-coated silica (D). Specifically,in the presence of the resulted component (d2) in the method (1), andthe component (d2) is added in the method (2), for example, and first,water generated in a condensation reaction with a dispersion medium inthe colloidal silica fine particles (d1) is azeotropically distilledunder normal pressure or reduce pressure at a temperature of 60 to 100°C., preferably 70 to 90° C., to give a solid concentration from 50 to90% by weight. Next, a non-polar solvent such as toluene is added intothe system, and a condensation reaction is conducted by stirring for 0.5to 10 hours while maintaining a solid concentration from 30 to 90% byweight, preferably from 50 to 80% by weight at a temperature of 60 to150° C., preferably 80 to 130° C., while azeotropically distilling thisnon-polar solvent, water and a dispersion medium of colloidal silicafine particles. In this procedure, a catalyst such as water, acid, baseand salt may be used for the purpose of promoting the reaction.

By use of the organic-coated silica (D) obtained by coating the surfaceof the hydrophilic colloidal silica fine particle obtained as describedabove with silicone for hydrophobization, in a curable composition(silica fine particle-containing hard coat material) for forming a hardcoat layer, compatibility with an ethylenically unsaturated compound (E)contained in the composition is improved, and a cured coated layerexcellent in transparency is obtained.

As the specific example of the ethylenically unsaturated compound (E),the same compounds as for the above-mentioned components (A) and (B) arelisted. Of them, particularly preferable are dipentaerythritolpentameth)crylate, dipentaerythritol hexa(meth)acrylate, pentaerythritoltri(meth)acrylate, pentaerythritol tetra(meth)acrylate,tris(2-(meth)acryloyloxyethyl)isocyanurate,bis(2-(meth)acryloyloxyethyl)hydroxyethyl isocyanurate,trimethylolpropane tri(meth)acrylate, urethane tri(meth)acrylateobtained by reacting 2-hydroxyethyl(meth)acrylate with trimer of1,6-hexamethylene diisocyanate, and urethane hexa(meth)acrylate obtainedby reacting an organic diisocyanate and pentaerythritoltri(meth)acrylate.

Into a curable composition for forming a hard coat layer (hereinafter,referred to as “hard coat layer curable composition”), it is preferableto add a photopolymerization initiator, for efficient curing with activeenergy ray. As the specific examples thereof, the same compounds asthose described above for the component (C) are listed. Of them,preferable are benzophenone, diethoxyacetophenone,2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal,1-hydroxycyclohexyl-1-phenylketone, benzoin methyl ether, benzoin ethylether, benzoin isopropyl ether, benzoin isobutyl ether,4,4-bis(diethylamino)benzophenone, 2,4,6-trimethylbenzophene,methyl-o-benzoyl benzoate, 4-phenylbenzophenone, thioxanetone,diethylthioxanetone, isopropylthioxanetone, chlorothioxanetone,t-butylanthraquinone, 2-ethylanthraquinone,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one andthiobenzoyl formate.

Further, to the hard coat layer curable composition, conventionallyknown various photo-sensitizers may be added such as methyl4-dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, amyl4-dimethylaminobenzoate and 4-dimethylaminoacetophenone, if necessary.Further, if necessary, various additives may be compounded such asorganic solvents, antioxidants, yellowing preventing agents, blueingagents, pigments, leveling agents, defoaming agents, thickening agents,precipitation inhibiting agents, antistatic agents, fogging preventingagents, ultraviolet absorbers and photo-stabilizer.

For painting of the hard coat layer curable composition, it ispreferable to compound an organic solvent from the standpoints ofviscosity control, and close adherence with a dispersion stabilizer andsubstrate, smoothness and uniformity of a cured coated layer. Thecompounding amount of an organic solvent is not particularly restricted,and preferably from 30 to 2000 parts by weight, more preferably from 50to 1000 parts by weight based on 100 parts by weight of the total amountof the components (D) and (E).

As the organic solvent, listed are, for example, alcohol-based,hydrocarbon-based, ketone-based, ether-based, ester-based, poly-hydricalcohol derivative-based, halogenated hydrocarbon-based organicsolvents. More specifically listed are alcohol-based solvents such asisopropyl alcohol, n-butanol, isobutanol and diacetone alcohol;hydrocarbon-based solvents such as hexane, cyclohexane, toluene, xyleneand aromatic solvents of high boiling point (Swazole 1000 and the like);ketone-based solvents such as methyl ethyl ketone (MEK), methyl isobutylketone (MIBK), diisobutyl ketone (DIBK) and cyclohexanone; ether-basedsolvents such as ethyl ether; ester-based solvents such as ethylacetate, n-butyl acetate, amyl acetate, methoxypropyl acetate andethoxyethyl acetate; poly-hydric alcohol derivative-based solvents suchas methylcellosolve, ethylcellosolve, butylcellosolve, methoxypropanol,methoxypropyl acetate, methoxybutanol and ethyl diglycol; and so on.These may be used singly or in admixture of two or more.

Of them, methoxypropanol and methoxypropyl acetate are particularlypreferable from the standpoints of the uniform solubility and dispersionstability of a hard coat layer curable composition, further, closeadherence with a substrate and the smoothness and uniformity of a coatedfilm. However, when these solvents are used, it is necessary toevaporate the solvent before conducting curing with active energy ray,after painting. The evaporation method is not particularly restricted,and heat treatment may be advantageously conducted at 20 to 120° C. for1 to 60 minutes using known means such as natural drying, infrareddrying and drying with a hot air furnace.

In the hard coat layer curable composition, a fluorine-based orsilicone-based slipping agent may be added for enhancing the slippingproperty of an optical disc and improving a scratch-preventing ability.As the slipping agent, polyether-modified silicone is suitable.

A supporting substrate of the optical disc of the present invention maybe transparent or opaque. As its material, known materials such asglass, ceramics, metals and plastics can be used. Of them, plastics arepreferable from the standpoint of easiness in molding a land and grooveof a cheap and light optical disc. Specific examples thereof includepolycarbonate-based resins, polymethyl methacrylate-based resins andamorphous polyolefin-based resins. Namely, it is preferable to use amolded article of such plastic materials, as a supporting substrate.

A recording layer of the optical disc of the present invention is notparticularly restricted, and conventionally known various materials forrecording can be used. For example, in the case of a reading-dedicatedoptical disc, metals showing high light reflection coefficient can beused such as gold, silver, silver alloy, aluminum and aluminum alloy, asthe material of a recording layer. Particularly, an aluminum alloy whichis cheap and showing high durability is preferable. For example, in thecase of a re-writable optical disc, listed as the material of a phasechange recording layer are silver.In.Te.Sb alloy, silver.In.Te.Sb.Gealloy, Ge.Sb.Te alloy, Ge.Sn.Sb.Te alloy and Sb.Te alloy, and listed asthe material of a photomagnetic recording layer are Tb.Fe.Co alloy andthe like. Further, a dielectric layer such as SiN, ZnS and SiO₂ may bestacked on these recording layers.

For forming a recording layer, known thin film forming technologies suchas a vacuum vapor deposition method, ion plating method and sputteringmethod may advantageously be used.

The present invention will be illustrated in detail below usingexamples. In the following descriptions, “parts” are by weight.

SYNTHESIS EXAMPLE 1 Production of Urethane Acrylate (UA1: Component A)

(1) Into a three-necked flask having an internal volume of 5 literequipped with a stirrer, thermoregulator, thermometer and condenser wascharged 1112 g (10 mol equivalent) of isophorone diisocyanate (DesmodurI manufactured by Sumitomo Bayer Urethane K.K., hydrolyzable chlorineamount: 60 ppm) and 0.5 g of dibutyltin dilaurate, and heated so thatthe inner temperature reached 70° C. with a water bath.

(2) Liquid prepared by uniformly mixing and dissolving 193 g (2.4 molequivalent) of N-methyl-N-(2-hydroxyethyl)-3-hydroxypropylamide and 1105g (2.6 mol equivalent) of polybutylene glycol (n=12, average molecularweight: 850) was charged into a dropping funnel equipped with a sidetube. The liquid in this dropping funnel was dropped at constant ratefor 4 hours with heating the content in the flask of the above-mentionedoperation (1) while maintaining the inner temperature of the flask at 65to 75° C., and the content was stirred at the same temperature for 2hours to cause reaction.

(3) Then, the temperature of the flask content was lowered to 60° C.,and liquid prepared by uniformly mixing and dissolving 581 g (5 molequivalent) of 2-hydroxyethyl acrylate and 1.5 g of hydroquinonemonomethyl ether, charged in a separate dropping funnel, was dropped atconstant rate for 2 hours while maintaining the inner temperature of theflask at 55 to 65° C. Then, they were reacted for 4 hours whilemaintaining the temperature of the flask content at 75 to 85° C., toobtain a urethane acrylate (UA1). Completion of the reaction was judgedby measurement of the remaining isocyanate equivalent, to confirm thatthe reaction ratio was 99% or more.

SYNTHESIS EXAMPLE 2 Production of Urethane Acrylate (UA2: Component A)

(1) Into a three-necked flask having an internal volume of 5 literequipped with a stirrer, thermoregulator, thermometer and condenser wascharged 1324 g (10 mol equivalent) of bis(4-isocyanatocyclohexyl)methane(Desmodur W manufactured by Sumitomo Bayer Urethane K.K., hydrolyzablechlorine amount: 4 ppm) and 0.5 g of dibutyltin dilaurate, and heated sothat the inner temperature reached 70° C. with a water bath.

(2) Liquid prepared by uniformly mixing and dissolving 70 g (0.8 molequivalent) of N-methyl-N-(2-hydroxyethyl)-4-hydroxybutylamide and 848 g(3.2 mol equivalent) of polycaprolactonediol (Placcel205 manufactured byDaicel Chemical Industries, Ltd., average molecular weight: 530) wascharged into a dropping funnel equipped with a side tube. The liquid inthis dropping funnel was dropped at constant rate for 4 hours withheating the content in the flask of the above-mentioned operation (1)while maintaining the inner temperature of the flask at 65 to 75° C.,and the content was stirred at the same temperature for 2 hours to causereaction.

(3) Then, the temperature of the flask content was lowered to 60° C.,and liquid prepared by uniformly mixing and dissolving 696 g (6 molequivalent) of 2-hydroxyethyl acrylate and 1.5 g of hydroquinonemonomethyl ether, charged in a separate dropping funnel, was dropped atconstant rate for 2 hours while maintaining the inner temperature of theflask at 55 to 65° C. Then, they were reacted for 4 hours whilemaintaining the temperature of the flask content at 75 to 85° C., toobtain a urethane acrylate (UA2). Completion of the reaction was judgedby measurement of the remaining isocyanate equivalent, to confirm thatthe reaction ratio was 99% or more.

SYNTHESIS EXAMPLE 3 Production of Urethane Acrylate (UA3: Component A)

(1) Into a three-necked flask having an internal volume of 5 literequipped with a stirrer, thermoregulator, thermometer and condenser wascharged 1112 g (10 mol equivalent) of isophorone diisocyanate and 0.5 gof dibutyltin dilaurate, and heated so that the inner temperaturereached 70° C. with a water bath.

(2) Liquid prepared by uniformly mixing and dissolving 161 g (2 molequivalent) of N-methyl-N-(2-hydroxyethyl)-3-hydroxypropylamide and 1303g (2.6 mol equivalent) of aliphatic polycarbonatediol (CX-4710manufactured by Asahi Chemical Industry Co., Ltd., average molecularweight: 1002) was charged into a dropping funnel equipped with a sidetube. The liquid in this dropping funnel was dropped at constant ratefor 4 hours with heating the content in the flask of the above-mentionedoperation (1) while maintaining the inner temperature of the flask at 65to 75° C., and the content was stirred at the same temperature for 2hours to cause reaction.

(3) Then, the temperature of the flask content was lowered to 60° C.,and liquid prepared by uniformly mixing and dissolving 626 g (5.4 molequivalent) of 2-hydroxyethyl acrylate and 1.5 g of hydroquinonemonomethyl ether, charged in a separate dropping funnel, was dropped atconstant rate for 2 hours while maintaining the inner temperature of theflask at 55 to 65° C. Then, they were reacted for 4 hours whilemaintaining the temperature of the flask content at 75 to 85° C., toobtain a urethane acrylate (UA3). Completion of the reaction was judgedby measurement of the remaining isocyanate equivalent, to confirm thatthe reaction ratio was 99% or more.

SYNTHESIS EXAMPLE 4 Production of Urethane Acrylate (UA4: Component B)

(1) Into a three-necked flask having an internal volume of 5 literequipped with a stirrer, thermoregulator, thermometer and condenser wascharged 867 g (7.8 mol equivalent) of isophorone diisocyanate and 0.5 gof dibutyltin dilaurate, and heated so that the inner temperaturereached 70° C. with a water bath.

(2) 1658 g (3.0 mol equivalent) of polybutylene glycol was charged intoa dropping funnel equipped with a side tube. The liquid in this droppingfunnel was dropped at constant rate for 4 hours with heating the contentin the flask of the above-mentioned operation (1) while maintaining theinner temperature of the flask at 65 to 75° C., and the content wasstirred at the same temperature for 2 hours to cause reaction.

(3) Then, the temperature of the flask content was lowered to 60° C.,and liquid prepared by uniformly mixing and dissolving 453 g (3.9 molequivalent) of 2-hydroxyethyl acrylate and 1.5 g of hydroquinonemonomethyl ether, charged in a separate dropping funnel, was dropped atconstant rate for 2 hours while maintaining the inner temperature of theflask at 55 to 65° C. Then, they were reacted for 4 hours whilemaintaining the temperature of the flask content at 75 to 85° C., toobtain a urethane acrylate (UA4). Completion of the reaction was judgedby measurement of the remaining isocyanate equivalent, to confirm thatthe reaction ratio was 99% or more.

SYNTHESIS EXAMPLE 5 Production of Urethane Acrylate (UA5: component B)

(1) Into a three-necked flask having an internal volume of 5 literequipped with a stirrer, thermoregulator, thermometer and condenser wascharged 1334 g (12 mol equivalent) of isophorone diisocyanate and 0.5 gof dibutyltin dilaurate, and heated so that the inner temperaturereached 70° C. with a water bath.

(2) Liquid prepared by uniformly mixing and dissolving 1416 g (12.2 molequivalent) of 2-hydroxyethyl acrylate and 1.5 g of hydroquinonemonomethyl ether was charged into a dropping funnel equipped with a sidetube. The liquid in this dropping funnel was dropped at constant ratefor 6 hours with heating the content in the flask of the above-mentionedoperation (1) while maintaining the inner temperature of the flask at 65to 75° C., and the content was stirred at the same temperature for 4hours to cause reaction, to obtain a urethane acrylate (UA5). Completionof the reaction was judged by measurement of the remaining isocyanateequivalent, to confirm that the reaction ratio was 99% or more.

SYNTHESIS EXAMPLE 6 Production of Epoxy Acrylate (EA1: component b1)

Into a three-necked flask having an internal volume of 2 liter equippedwith a stirrer, thermoregulator, thermometer and condenser was charged958 g of bisphenol A type epoxy resin (Epikote 1001 manufactured by YukaShell Epoxy K.K., epoxy equivalent: 479), 144 g of acrylic acid, 11 g ofdimethylaminoethyl methacrylate, 78.6 g of tetrahydrofurfuryl acrylate,1.1 g of hydroquinone monomethyl ether and 0.5 g of2,6-di-tertiary-butyl-4-methylphenol, and they were reacted at 95° C.for 24 hours. Completion of the reaction was conducted by measurement ofacid value, and it was confirmed that the acid value was 1 mg KOH/g, anda mixture of 80% by weight of bisphenol A type epoxy acrylate (EA1) and20% by weight of tetrahydrofurfuryl acrylate was obtained. The resultedmixture was subjected for GPC measurement, to find that theweight-average molecular weight of the epoxy acrylate (EA1) was 2360.

SYNTHESIS EXAMPLE 7 Production of Epoxy Acrylate (EA2: Component b1)

Into a three-necked flask having an internal volume of 5 liter equippedwith a stirrer, thermoregulator, thermometer and condenser was charged756 g of bisphenol A type epoxy resin (Epikote 828 manufactured by YukaShell Epoxy K.K., epoxy equivalent: 189), 288 g of acrylic acid, 10.4 gof dimethylaminoethyl methacrylate, 263.9 g of tetrahydrofurfurylacrylate, 1 g of hydroquinone monomethyl ether and 0.5 g of2,6-di-tertiary-butyl-4-methylphenol, and they were reacted at 95° C.for 24 hours. Completion of the reaction was conducted by measurement ofacid value, and it was confirmed that the acid value was 1 mg KOH/g, anda mixture of 80% by weight of bisphenol A type epoxy acrylate (EA2) and20% by weight of tetrahydrofurfuryl acrylate was obtained. The resultedmixture was subjected for GPC measurement, to find that theweight-average molecular weight of the epoxy acrylate (EA2) was 700.

SYNTHESIS EXAMPLE 8 Production of Photo-Curable Silicone (CS1: ComponentD)

Into a four-necked flask having an internal volume of 3 liter equippedwith a stirrer, thermometer and condenser was charged 2000 parts ofisopropanol silica sol (dispersing medium: isopropanol, SiO₂concentration: 30 wt %, primary particle size: 12 mμ, trade name:IPA-ST, manufactured by Nissan Chemical Industries, Ltd., herein afterreferred to as “IPA-ST”) and 382 g of3-methacryloyloxypropyltrimethoxysilane (trade name: TSL-8370,manufactured by Toshiba Silicon K.K., herein after referred to as“TSL-8370”), and the mixture was heated while stirring, and 150 parts ofdistilled water was gradually dropped simultaneously with initiation ofreflux of a volatile component. After completion of dropping, hydrolysiswas conducted while stirring for 2 hours under reflux.

After completion of hydrolysis, volatile components such as alcohol andwater were distilled under normal pressure, and 600 parts of toluene wasadded when the concentration of solid content (600 parts of SiO2 ofIPA-ST and 317 parts of TSL-8370, total 917 parts) was about 60% byweight, and alcohol and water were azeotropically distilled togetherwith toluene. Next, 1500 parts of toluene was added in separateportions, solvent substitution was completely conducted, to give atoluene dispersion system. At this stage, the solid concentration wasabout 40% by weight.

Further, a reaction was conducted at 110° C. for 4 hours whiledistilling toluene, to give a solid concentration of about 60% byweight. Thereafter, 100 parts of methoxypropanol was further added,toluene was distilled off to conduct solvent substitution, giving amethoxypropanol dispersion system.

The resulted photo-curable silicone (hereinafter, referred to as “SC-1”)was yellow, transparent and viscous liquid as Newtonian fluid, and had aviscosity at 25° C. of 30 mP·s. The solid concentration was 58% byweight as the heated residue. This heated residue is represented by[weight (g) after heating/weight (g) before heating]×100 (wt %), and theheating condition include 105° C. and 3 hours.

Using the compounds obtained in the above-mentioned Synthesis Examples 1to 4, the following examples was conducted. “Skew” in the examples meansthe maximum tilt angle along radius direction to the opticaltransmittance layer side at the outermost periphery of an optical disc.

EXAMPLE 1

(1) Preparation of Active Energy Ray Curable Composition for Formationof Optical Transmittance Layer:

50 parts of the urethane acrylate (UA1) obtained in Synthesis Example 1as the component (A), 18.75 parts of a mixture of the bisphenol A typeepoxy acrylate (EA1) and tetrahydrofurfuryl acrylate, as the component(B) (15 parts of EA1, and 3.75 parts of tetrahydrofurfuryl acrylate),16.25 parts of tetrahydrofurfuryl acrylate, 15 parts of isobonylacrylate, and 2 parts of 1-hydroxycyclohexylphenylketone as thecomponent (C) were mixed and dissolved, to obtained a active energy raycurable composition for formation of optical transmittance layer (forcoating optical disc).

The resulted composition was colorless and transparent and was viscousliquid having a viscosity at normal temperature (25° C.) of about 6000mPa·s. The volume shrinkage coefficient was calculated from the liquidspecific gravity of the composition and the solid specific gravity ofthe cured substance, as a result, it was 6.5%. In its evaluation, volumeshrinkage coefficient of 7.5% or less was permissible range.

(2) Production and Evaluation of Optical Disc for Evaluation

On a transparent disc substrate (diameter: 12 cm, plate thickness: 1.2mm, tilt angle: 0°) in optical disc shape obtained by injection moldingof a polycarbonate resin (Panlite AD 9000TG manufactured by Teijin KaseiK.K.), an aluminum alloy was sputtered to give a thickness of 50 nm by asputtering apparatus CDI-900 manufactured by Balzers K.K., to obtain anoptical disc having an aluminum alloy reflection membrane as a recordinglayer. On the aluminum alloy reflection membrane of this optical disc,the above-mentioned curable composition was coated using a spin coaterto give an average thickness of 100 μm. This coated membrane was curedby a high pressure mercury lamp (120 W/cm) having a lamp height of 10 cmat energy quantity of an accumulated light quantity of 1000 mJ/cm², toobtain an optical disc for evaluation having an optical transmittancelayer (cured coating layer) of the above-mentioned curable composition.

The tilt angle of this optical disc was measured using an optical diskoptical mechanical property measuring apparatus (DLD-3000, manufacturedby Japan EM K.K.) under environments of 20° C. and 50% RH, to find thatthe tilt angle of 0.1°, showing excellent mechanical property. Further,this optical disc was aged under environments of 80° C. and 85% RH for100 hours, then, removed and left under environments of 20° C. and 50%RH for 100 hours, and the tilt angle was measured again, to find thatthe tilt angle of 0.2°, showing excellent mechanical property. Thepermissible range of the tilt angle was from 0 to 0.30° both at theinitiation and after the durability test.

The aluminum alloy surface was observed at a magnification of 800 by amicroscope, as a result, corrosions such as whitening and pinhole didnot occur, showing excellent recording layer protective ability.

According to JIS K-5400, the pencil hardness of the cured coating layerwas measure to find it was B, harder than a polycarbonate substrate(pencil hardness: 4B) and regarded as excellent. The permissible rangeof pencil hardness was 2B or more.

A cured coating layer was peeled at mirror portion of an aluminum alloysurface of an optical disc obtained in the same manner, and the beamtransmission of the resulted transparent layer was measured using aspectral photometer U-3400 manufactured by Hitachi, Ltd. at a wavelengthof 400 nm to find that it was 85%, meaning excellent beam transmittance.The permissible range of beam transmittance was 70% or more.

EXAMPLES 2 TO 7, COMPARATIVE EXAMPLES 1 TO 4

Optical discs for evaluation were produced in the same manner exceptingthat curable compositions shown in Table 1 were used, and evaluated inthe same manner. The results are shown in Table 1.

TABLE 1 Example Comparative Example 1 2 3 4 5 6 7 1 2 3 4 CurableComponent UA1 50 55 60 60 65 composition (A) UA2 60 UA3 45 Component EA115 15 (B) EA2 10 UA4 50 UA5 60 M315 10 10 10 10 70 M313 15 5 5 THFA 2025 20 20 20 25 20 25 30 5 IBXA 15 5 5 15 5 TCA 5 TCDA 15 TMPFA 15 MEDOA10 NPGDA 40 C9DA 15 TMPTA 10 10 45 Component HCPK 2 2 2 2 2 3 3 2 2 2(C) BNP 6 EPA 3 Viscosity of 6000 6300 5000 2500 3000 3400 5300 30003500 160 25 composition (mPa · s) Evaluation Beam transmittance (%) 8588 88 88 88 88 88 85 89 85 57 results Pencil hardness B B B B B B B 6BHB 2H H Volume shrinkage 6.5 6.1 7 6.5 6.6 6.5 6.3 6.5 8 10 12.5coefficient (%) Initial tilt angle (°) 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.10.4 Note 1 Note 1 Tilt angle after test 0.2 0.2 0.25 0.2 0.2 0.2 0.2 0.20.9 Note 1 Note 1 Corrosion resistance Good Good Good Good Good GoodGood Good Good Good Good

Abbreviations in Table 1 are as described below.

-   Note: Tilt angle is by far out of the measurement possible range    (±1) of a measuring apparatus, and measurement is impossible.-   UA1: urethane acrylate obtained in Synthesis Example 1 (UA1)-   UA2: urethane acrylate obtained in Synthesis Example 2 (UA2)-   UA3: urethane acrylate obtained in Synthesis Example 3 (UA3)-   EA1: epoxy acrylate obtained in Synthesis Example 6 (EA1)-   EA2: epoxy acrylate obtained in Synthesis Example 7 (EA2)-   UA4: urethane acrylate obtained in Synthesis Example 4 (UA1)-   UA5: urethane acrylate obtained in Synthesis Example 5 (UA1)-   M315: acrylate manufactured by Toagosei Co., Ltd. (mixture of 90% of    tris(2-acryloyloxyethyl)isocyanurate and 10% of    bis(2-acryloyloxyethyl)hydroxyethyl isocyanurate)-   M313: acrylate manufactured by Toagosei Co., Ltd. (mixture of 65% of    tris(2-acryloyloxyethyl)isocyanurate and 35% of    bis(2-acryloyloxyethyl)hydroxyethyl isocyanurate)-   THFA: tetrahydrofurfuryl acrylate-   IBXA: isobonyl acrylate-   TCA: tricyclodecanyl acrylate-   TCDA: tricyclodecane dimethanol diacrylate-   TMPFA: trimethylolpropane formal monoacrylate-   MEDOA: 2-methyl-2-ethyl-1,3-dioxolanylmethyl acrylate-   NPGDA: neopentyl glycol diacrylate-   C9DA: 1,9-nonanediol diacrylate-   TMPTA: trimethylolpropane triacrylate-   HCPK: 1-hydroxy-cyclohexylphenylketone-   BNP: benzophenone-   EPA: ethyl p-dimethylaminobenzoate

EXAMPLE 8

An optical disc for evaluation was produced in the same manner as inExample 1 except that the curable composition in Example 2 was used andpure silver (purity: 99.99%) was used as a sputtering target, andevaluated in the same manner. In this example, excellent valuesequivalent to those in Example 1 were obtained in all of beamtransmittance, mechanical property, pencil hardness, initial tilt angle,tilt angle after test, and corrosion resistance.

EXAMPLE 9

(1) Preparation of Curable Composition for Hard Coat Layer:

86.2 parts of the photo-curable silicone (CS1) obtained in SynthesisExample 8 (containing 50 parts of solid component and 36.2 parts ofpropylene glycol monomethyl ether as a solvent component) as thecomponent (D), 47 parts of dipentaerythritol hexaacrylate as thecomponent (E), 6 parts of a photopolymerization initiator (Irgacure 184,manufactured by Chiba Specialty Chemicals K.K.) as the component (C) and3 parts of polyether-modified silicone L-7001 manufactured by NipponUnicar K.K. were mixed and dissolved, to obtain a curable compositionfor hard coat layer.

(2) Formation of Hard Coat Layer and Evaluation Thereof:

On the optical transmittance layer of the optical disc for evaluationobtained in Example 1, the above-mentioned curable composition for hardcoat layer was painted using a spin coated to give an average thicknessof 2 μm, and left for 1 minute at room temperature, and methoxypropanolcontained in the composition was evaporated. Thereafter, this coatedlayer was cured by a high pressure mercury lamp (120 W/cm) having a lampheight of 10 cm at energy quantity of an accumulated light quantity of1000 mJ/cm², to obtain an optical disc having a recording layer, opticaltransmittance layer and hard coat layer.

The tilt angle of this optical disc was measured using an optical diskoptical mechanical property measuring apparatus (DLD-3000, manufacturedby Japan EM K.K.) under environments of 20° C. and 50% RH, to find thatthe tilt angle of 0.51°, showing excellent mechanical property. Further,this optical disc was left under environments of 80° C. and 85% RH for100 hours, then, removed and left under environments of 20° C. and 50%RH for 100 hours, and the tilt angle was measured again, to find thatthe tilt angle of 0.25°, showing excellent mechanical property.

Further, after this test, the aluminum alloy surface was observed at amagnification of 800 by a differential interference microscope, as aresult, corrosions such as whitening and pinhole did not occur, showingexcellent protective ability.

According to JIS K-5400, the pencil hardness of the cured coating layerwas measure to find it was F, and the layer was not scratched even ifabraded with steel wool #0000, showing very excellent abrasion scratchresistance.

A protective layer and a hard coat layer were peeled as an integratedbody from an aluminum alloy surface of an optical disc obtained in thesame manner, and the beam transmission of the resulted transparent layerwas measured using a spectral photometer U-3400 manufactured by Hitachi,Ltd. at a wavelength of 400 nm to find that it was 85%, meaningexcellent beam transmittance.

INDUSTRIAL APPLICABILITY

As described above, the composition of the present invention can form acured coating layer showing low volume shrinkage coefficient inpolymerization, having excellent transparency, and having excellenthardness, recording layer protective ability and mechanical property. Bythis composition, for example, it is possible to obtain a high densitytype optical disc having an optical transmittance layer of about 100 μm.This optical disc is extremely useful as an optical disc for conductedreading and/or writing using blue laser.

1. An optical disc, comprising: a substrate carrying thereon a recordinglayer and a cured coating layer laminated in this order in which thecured coating layer acts as an incident side surface for recording lightand/or reading light from a laser having a shorter wavelength than awavelength of a red laser, wherein the cured coating layer is a layerobtained by curing a curable composition comprising a urethane(meth)acrylate and a compound (b2) of the following general formula (I):

wherein X₁ and X₂ represent an acryloyloxy group or methacryloyloxygroup, X₃ represents a hydroxy group, acryloyloxy group ormethacryloyloxy group, and R₁, R₂ and R3 represent an alkyl group having1 to 4 carbon atoms, said curable composition having a volume shrinkagecoefficient of 7.5% or less, a pencil hardness of 2B or more, athickness of from 50 to 150 μm, and having a beam transmittance in thewavelength range from 380 to 800 nm of 75% or more.
 2. The optical discaccording to claim 1, wherein curable composition contains a urethane(meth)acrylate compound (A) having at least one amide group in themolecule, an ethylenically unsaturated compound (B) other than theurethane (meth)acrylate compound (A) and a photopolymerization initiator(C), in which the compound (B) comprises the compound (b2).
 3. Theoptical disc according to claim 2, wherein the urethane (meth)acrylatecompound (A) is a urethane (meth)acrylate obtained by reacting thefollowing components (a1) to (a4): (a1) an amide-containing compoundhaving at least one amide group and at least two hydroxy groups in themolecule, (a2) a poly-hydric alcohol compound other than said component(a1), (a3) a diisocyanate compound, (a4) a hydroxy group-containing(meth)acrylate.
 4. The optical disc according to claim 1, wherein a hardcoat layer is laminated on the cured coating layer.
 5. The optical discaccording to claim 4, wherein the hard coat layer is a layer obtained bycuring a curable composition containing organic-coated silica (D)obtained by condensation of colloidal silica fine particles (d1) and ahydrolysis product (d2) of an organic silane compound.
 6. The opticaldisc according to claim 5, wherein the hydrolysis product (d2) is asilanol compound obtained by hydrolysis of a monomer of the followinggeneral formula (II):

wherein, X represents a methacryloyloxy group, acryloyloxy group, styrylgroup or vinyl group, R₄ represents a direct bond or a linear orbranched alkyl group having 1 to 8 carbon atoms, R₅ and R₆ represent alinear or branched alkyl group having 1 to 8 carbon atoms, a representsan integer of 1 to 3, b represents an integer of 0 to 2, and a+brepresents an integer of 1 to
 3. 7. The optical disc according to claim4, wherein the thickness of the hard coat layer is from 0.1 to 5 μm. 8.The optical disc according to claim 4, wherein the beam transmittance oftwo layers of the cured coating layer and hard coat layer within thewavelength range from 380 to 800 nm is 70% or more.
 9. The optical discaccording to claim 1, wherein the curable composition contains 20 to 80%by weight of the urethane (meth)acrylate and, 20 to 80% by weight of anethylenically unsaturated compound (B) other than the urethane(meth)acrylate compound (A), in which the compound (B) comprises thecompound (b2).